How do you know if you've found a genuine new species? Zoologist Mark Siddall explains.

You're out in the wilderness — or maybe just your front yard — and you see a really weird animal. It's like a cross between a bat and a frog. Have you discovered a new species? If so, how would you prove it?

We asked American Museum of Natural History zoologist Mark Siddall for some advice. So before you cry cryptid, you'll want to know what a real scientist would do in the face of the unknown.

Mongolian Death Worm painting by Pieter Dirkx

How do you know if you've found a genuine new species? Zoologist Mark Siddall explains.

Siddall is a world expert in leeches (as you can see from the friends on his arm in this picture). This has by necessity made him an expert in discovering new species. So few scientists study leeches that Siddall's concerted effort to hunt for them has turned up several new species over the years. In fact, before Siddall began his work, he marveled, "there was no phylogeny of leeches" — no basic tree of life for the creatures, showing which species was related to which.

So how do you know when you've stumbled across a new species? Siddall said it's not an exact science, though most biologists agree that a new species is simply a distinctive creature with its own evolutionary lineage and unique gene pool.

Get a specimen
Before anyone can claim a new species, however, they must have at least one specimen of it, and probably several. Often scientists will prove that their species is "distinct" by comparing it to other specimens that are closely related to it. Explained Siddall:

Any new species name requires a number of specimens, and it must reside in a natural history museum. Suppose I got to Africa and found a long-necked spotted mammal and named it Joshuacus Shankenburgicus. How would we adjudicate whether or not I had just given a new name to a giraffe? We'd go to the typed specimen of Giraffa camelopardalis, which happens to be in a natural history museum wrapped in linen, and compare them.

Give it a name and describe it
Names are actually quite important to the process of claiming your new species. "I look at a species name as a hypothesis," said Siddall. "We don't have proof of anything – we have ideas, and corroboration, and some ideas are better corroborated. So a species name is a hypothesis about a distinction between species."

But don't expect your nicely-named batfrog to become a new species without some intensive examination from scientists. "I could find a new leech every day and give it a name," joked Siddall. "But I would incur the wrath and disdain of my colleagues, so there's self- and community-policing. There's peer review." By the same token, it's not a good idea to spend too much time wringing one's hands over whether something a new species or not — after all, these names are hypotheses, and if they're proven wrong later then that's just science at work. "If I had to test every species against rigid species guidelines I'd be breeding leeches with donkeys," Siddall laughed. "I think if the distinctiveness is obvious enough, then it's within one's rights to put forward the name of a new species. Sure, it's possible that it's just a mutant or that it had too much tungsten in its diet. All we try to do is explain the world around us." And that's what it means to name a new species: It's a description.

But aren't there some hard and fast rules for declaring a new species? Can't we just agree on some set guidelines? Absolutely not, argued Siddall:

The rules for naming a new species were established about a century ago, but if we used those rules today we couldn't use confocal data and DNA because that technology didn't exist. It would be an authoritarian code not authoritative. The rules of taxonomy have to be flexible in terms of data brought to bear, while still having basic guidelines.

Those "basic guidelines" are pretty simple: You need a description of the species, a name, and some specimens.

How do you know if you've found a genuine new species? Zoologist Mark Siddall explains.

How do you find new species?
Siddall said that finding a new species can be surprisingly easy sometimes:

Take the Tyrannobdella rex leech. It had one jaw instead of three, and 8 enormous teeth instead of 100 tiny ones. We'd never seen anything like it before. We checked the scientific literature, and to the best of our knowledge nobody had seen a leech with an enormous jaw and 8 enormous teeth. We were compelled to write a new genus and a new species. It was very straightforward.

But other species can be harder to differentiate. "You might only be looking at subtle differences in gonads and salivary glands," Siddall said.

So what's the best way to hunt for new species? Siddall explains his technique for discovering new kinds of leeches:

Our standard method of collecting leeches is to get in the water and wait for them. We know we're successful when we get first blood. You get to an area, and first you spend time trying to find out about the local waterways and jungles. You develop a gestalt for how local leeches are behaving. Are they on the banks in ponds, in the middle of the river, in the cool or hot parts of the jungle? Because you don't know when the first [leech] is coming, invariably the first one's got you before you know. It always draws blood because you didn't know it was coming. Once you've found that first one then you know you've succeeded.

He added that it's very easy to get leeches off your body — "just brush them aside, and they come off easily," he explained. And that leaves them alive, too, which is crucial for specimen-gathering.

How do you know if you've found a genuine new species? Zoologist Mark Siddall explains.

Scientists who find new species often have a soft spot for cryptids, or mystery animals. Siddall admitted that two years ago during a meeting of parasitologists he went on a hunt for a mythical giant leech called Tlanusi, said to live in the Hiwassee River near Tennessee. "It had been described in Cherokee myth," Sidall said. "And I thought, 'Let's go look for this leech!' I used my usual method of collecting, and climbed right into the river." He paused dramatically. "What happened was that I didn't find it. But maybe that for the best, because if you lay eyes on it you turn to dust."

Mark Siddall will be a judge in io9's Cryptid Summer bounty, where we'll give you $2000 for evidence that you've discovered a genuine cryptid, or new species.

How do you know if you've found a genuine new species? Zoologist Mark Siddall explains.

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